Trump is doubling down on his claims that Amazon uses the US Postal Service as a 'delivery boy,' and it could be a major blow to countless American businesses (AMZN)

Jae C. Hong/AP Images President Donald Trump doubled down on his claims that Amazon is abusing its relationship with the US Postal Service, saying the company is turning the USPS into a "delivery boy," in a tweet on Monday. The USPS' low fixed costs and mandate to deliver mail to Americans makes it an ideal option for "last-mile" delivery, something that has served Amazon well. However, Amazon is far from being the only American company that benefits from the USPS' current pricing plan. Presiden...